The present invention relates to a method for alarming a decrease in tire air-pressure and an apparatus used therefore. More particularly, it relates to a method for alarming a decrease in tire air-pressure and an apparatus used therefore wherein a threshold for judging a decompressed condition and a setting for a time required for judging the decompressed condition are varied prior and after start of driving to thereby improve the accuracy of detecting a decompressed condition.
While one possible factor causing decrease in internal pressure of a tire is minute leakage of air from between rubber molecules of the tire, it is mostly the case that decreases in internal pressure are caused through damages of tire units, rims or tire valves which are component members of tires. Speeds at which internal pressures are decreased caused by a nail piercing through a tire, which is the most occurring factor, have so far been reported upon performing various experiments.
JAF MATE, June 1995 edition includes a report of results about experiments performed for testing air-pressure decreasing speeds in case of blowouts of tires caused through nails. According to this article, a tire with a normal internal pressure of 2.1 kgf/cm2 (2.06xc3x97104 Pa) was used, and the internal pressure decreased only to 1.95 kgf/cm2 (1.91xc3x97104 Pa) (decrease of approximately 7%) upon elapse of as much as 5 hours in case the nail remained in the tire. Also in case the nail was removed, the internal pressure decreased to only 1.90 kgf/cm2 (1.86xc3x97104 Pa) (decrease of approximately 10%) after elapse of 1 hour and to only 1.65 kgf/cm2 (1.62xc3x97104 Pa) (decrease of approximately 21%) after elapse of 5 hours.
On the other hand, it was found that the air-pressure remained at 2.60 kgf/cm2 (2.55xc3x97104 Pa) after driving for 2 hours under a condition where a nail having a diameter of 3.1 mm and a length of 65 mm was pierced through a tread block portion of a tire having a tire size of 215/70R15 and a normal internal pressure of 2.60 kgf/cm2 (2.55xc3x97104 Pa). When measuring the internal pressure of the tire when the vehicle was halting at an interval of 15 seconds after removing this nail, the internal pressure decreased to 1.90 kgf/cm2 (1.86xc3x97104 Pa)(decrease by approximately 27%) after elapse of 60 seconds and to 1.35 kgf/cm2 (1.32xc3x97104 Pa) (decrease by approximately 48%) after elapse of 120 seconds. These results indicate remarkably faster internal pressure decreasing speeds than compared to the test of JAF.
While there is presently no clear definition as to a degree of decrease in internal pressure at which the vehicle becomes dangerous, it will at least not become impossible to drive owing to the damage of the tire although cornering performances will become inferior when the decrease in internal pressure is approximately 40%. Thus, by setting this degree of compression as a target value, it will be possible to inform the driver of danger caused through a decrease in internal pressure of a tire if it would be possible to detect a decrease in air-pressure within a time of 60 seconds although the air-pressure decreasing speed is fast as illustrated in FIG. 5.
However, since decreases in internal pressure of a tire will progress not only during driving but also during halting, decompression might gradually progress over night upon parking one""s vehicle without knowing that a blowout has occurred during driving to find out on the next morning that the tire is largely decompressed when starting driving.
In the case of a vehicle which had not been moved for a long time, tires might be largely decompressed owing to natural decompression when starting driving of the vehicle.
On the other hand, according to conventional methods for estimating decompression of a tire based on revolution velocities of tires (see, for instance, Japanese Unexamined Patent Publication No. 305011/1988), a decrease in tire air-pressure cannot be detected unless the tires are rotating, that is, unless the vehicle is running so that it might take several tens of seconds for detecting decompression even if the degree of decompression is large.
The present invention has been made in view of these facts, and it is an object thereof to provide a method for alarming decrease in tire air-pressure and an apparatus used therefor with which it is possible to detect a largely decompressed condition before start of running to thereby improve the accuracy of detecting decompression. It should be noted that a xe2x80x9cbefore-start-of-runningxe2x80x9d condition indicates a condition prior to throwing of a power source of the apparatus, which is generally a condition prior to turning an ignition switch ON.
In accordance with the present invention, there is provided a method for alarming decrease in tire air-pressure for judging a decrease in internal pressure of a tire attached to a four-wheeled vehicle and for accordingly generating alarm, wherein a threshold for judging decompression is set to be larger immediately after switching an ignition key ON when compared to a threshold for the vehicle in a normal running condition, decompression is judged in a decompression judging time which is shorter than a time for the vehicle in a normal running condition, and the threshold for judging decompression and the decompression judging time are returned to those for the normal running condition of the vehicle in case no decompression is judged.
In accordance with the present invention, there is also provided an apparatus for judging a decrease in internal pressure of a tire attached to a four-wheeled vehicle and for accordingly generating an alarm, comprising a velocity detecting means for detecting a velocity signal of respective tires, a judging means for performing calculating processes of a decompression judgement value for comparing a difference of two diagonal sums of rotational information of front wheel tires and rotational information of rear wheel tires based on rotational information obtained from the velocity signals detected by the velocity detecting means, an initial judging means for setting a threshold for judging decompression to be larger immediately after switching an ignition key ON when compared to a threshold for the vehicle in a normal running condition and judging decompression in a decompression judging time which is shorter than a time for the vehicle in a normal running condition, and a returning means for returning the threshold for judging decompression and the decompression judging time to those for the normal running condition of the vehicle in case no decompression is judged.
In accordance with the present invention, there is further provided a method for judging a decrease in internal pressure of a tire attached to a four-wheeled vehicle and for accordingly generating an alarm, comprising the steps of setting a threshold for judging decompression to be larger immediately after switching an ignition key ON when compared to a threshold for the vehicle in a normal running condition and judging decompression in a decompression judging time which is shorter than a time for the vehicle in a normal running condition; judging whether the vehicle is running on a bad road while a decompressed condition is judged during the short decompression judging time; and increasing a number of data used for judging decompression than compared to a number of data which might be incorporated during the short decompression judging time in case it is judged that the vehicle is running on a bad road.
In accordance with the present invention, there is yet further provided an apparatus for judging a decrease in internal pressure of a tire attached to a four-wheeled vehicle and for accordingly generating alarm, comprising a velocity detecting means for detecting a velocity signal of respective tires, a judging means for performing calculating processes of a decompression judging value for comparing a difference of two diagonal sums of rotational information of front wheel tires and rotational information of rear wheel tires based on rotational information obtained from the velocity signals detected by the velocity detecting means, an initial judging means for setting a threshold for judging decompression to be larger immediately after switching an ignition key ON when compared to a threshold for the vehicle in a normal running condition and judging decompression in a decompression judging time which is shorter than a time for the vehicle in a normal running condition, a bad road judging means for judging whether the vehicle is running on a bad road while a decompressed condition is judged during the short decompression judging time, and a data updating means for increasing a number of data used for judging decompression than compared to a number of data which might be incorporated during the short decompression judging time in case it is judged that the vehicle is running on a bad road.